Unimpaired function of a naturally occurring C terminally truncated vif gene product of human immunodeficiency virus type 1

Analysis of the percentage of human immunodeficiency virus type 1 sequences that are hypermutated and markers of disease progression in a longitudinal cohort, including one individual with a partially defective Vif

Hypermutation, the introduction of excessive G-to-A substitutions by host proteins in the APOBEC family, can impair replication of the human immunodeficiency virus (HIV). Because hypermutation represents a potential antiviral strategy, it is important to determine whether greater hypermutation is associated with slower disease progression in natural infection. We examined the level of HIV-1 hypermutation among 28 antiretroviral-naive Kenyan women at two times during infection. By examining single-copy gag sequences from proviral DNA, hypermutation was detected in 16 of 28 individuals. Among individuals with any hypermutation, a median of 15% of gag sequences were hypermutated (range, 5 to 43%). However, there was no association between the level of gag hypermutation and the viral load or CD4 count. Thus, we observed no overall relationship between hypermutation and markers of disease progression among individuals with low to moderate levels of hypermutation. In addition, one individual sustained a typical viral load despite having a high level of hypermutation. This individual had 43% of gag sequences hypermutated and harbored a partially defective Vif, which was found to permit hypermutation in a peripheral blood mononuclear cell culture. Overall, our results suggest that a potential antiviral therapy based on hypermutation may need to achieve a substantially higher level of hypermutation than is naturally seen in most individuals to impair virus replication and subsequent disease progression.

Population level analysis of human immunodeficiency virus type 1 hypermutation and its relationship with APOBEC3G and vif genetic variation

APOBEC3G and APOBEC3F restrict human immunodeficiency virus type 1 (HIV-1) replication in vitro through the induction of G-->A hypermutation; however, the relevance of this host antiviral strategy to clinical HIV-1 is currently not known. Here, we describe a population level analysis of HIV-1 hypermutation in [corrected] clade B proviral DNA sequences (n = 127). G-->A hypermutation conforming to expected APOBEC3G polynucleotide sequence preferences was inferred in 9.4% (n = 12) of the HIV-1 sequences, with a further 2.4% (n = 3) conforming to APOBEC3F, and was independently associated with reduced pretreatment viremia (reduction of 0.7 log(10) copies/ml; P = 0.001). Defective vif was strongly associated with HIV-1 hypermutation, with additional evidence for a contribution of vif amino acid polymorphism at residues important for APOBEC3G-vif interactions. A concurrent analysis of APOBEC3G polymorphism revealed this gene to be highly conserved at the amino acid level, although an intronic allele (6,892 C) was marginally associated with HIV-1 hypermutation. These data indicate that APOBEC3G-induced HIV-1 hypermutation represents a potent host antiviral factor in vivo and that the APOBEC3G-vif interaction may represent a valuable therapeutic target.

Amino acid residues 88 and 89 in the central hydrophilic region of human immunodeficiency virus type 1 Vif are critical for viral infectivity by enhancing the steady-state expression of Vif

A hydrophilic region consisting of strikingly clustered charged amino acids is present at the center of human immunodeficiency virus type 1 (HIV-1) Vif. In this study, the role for this central hydrophilic region (E(88)WRKKR(93)) in the virus replication in nonpermissive H9 cells was investigated by extensive deletion and substitution analysis. A total of 31 mutants were constructed. Deletion of the E(88) or W(89) residue alone abolished viral infectivity in H9 cells and impaired virus replication in primary macrophage cultures. Substitution analysis indicated that the hydrophilicity and charge of the central region are insignificant for the function of Vif. Of the 16 substitution mutants, 3 mutants with substitution of E(88) and W(89) with an A residue did not grow in H9 cells. Upon transfection, four mutants (i.e., two mutants with deletion of E(88) or W(89); a mutant with substitution of E(88) and W(89) with A; and a mutant with substitution of E(88), W(89), and R(90) with A) were found to express Vif at a very reduced level relative to that by the wild-type clone. These results have thus demonstrated that amino acid residues 88 and 89 of Vif are critical for the replication of HIV-1 in target cells by enhancing the steady-state expression of Vif. In addition, E(88) and W(89) residues were found to be extremely conserved among the Vif proteins of naturally occurring HIV-1 field isolates as well as those of laboratory HIV-1 strains.

Apparent lack of trans-dominant negative effects of various vif mutants on the replication of HIV-1

The vif gene of human immunodeficiency virus type 1 (HIV-1) is essential for virus growth in non-permissive cells such as H9. To elucidate the mechanism of action of the Vif protein, vif mutants, which show trans-dominant negative effects on the replication of HIV-1, would be useful tools. In this study, a new assay system to identify the mutants of this category was established. For this new system, various reporter clones carrying both mutant and authentic vif sequences were generated. By determining the growth ability of the viruses derived from the reporter constructs, the potential negative effect of the mutant vif sequence was readily and sensitively monitored. Ten vif mutant sequences tested were found not to exert the trans-dominant negative effect on the replication of HIV-1.

Intravirion processing of the human immunodeficiency virus type 1 Vif protein by the viral protease may be correlated with Vif function

The human immunodeficiency virus type 1 (HIV-1) Vif protein is specifically packaged into virus particles through an interaction with viral genomic RNA in which it associates with the viral nucleoprotein complex. We now demonstrate for the first time that virus-associated Vif is subject to proteolytic processing by the viral protease (Pr). Pr-dependent processing of Vif was observed both in vivo and in vitro. In vivo processing of Vif was cell type independent and evident by the appearance of a 7-kDa processing product, which was restricted to cell-free virus preparations. Processing of Vif required an active viral Pr and was sensitive to Pr inhibitors such as ritonavir. The processing site in Vif was characterized both in vivo and in vitro and mapped to Ala(150). Interestingly, the Vif processing site is located in a domain that is highly conserved among HIV-1, HIV-2, and simian immunodeficiency virus Vif isolates. Mutations at or near the processing site did not affect protein stability or packaging efficiency but had dramatic effects on Vif processing. In general, mutations that markedly increased or decreased the sensitivity of Vif to proteolytic processing severely impaired or completely abolished Vif function. In contrast, mutations at the same site that had little or no effect on processing efficiency also did not influence Vif function. None of the mutants affected the ability of the virus to replicate in permissive cell lines. Our data suggest that mutations in Vif that cause a profound change in the sensitivity to Pr-dependent processing also severely impaired Vif function, suggesting that intravirion processing of Vif is important for the production of infectious viruses.

Fully functional, naturally occurring and C-terminally truncated variant human immunodeficiency virus (HIV) Vif does not bind to HIV Gag but influences intermediate filament structure

A variant human immunodeficiency virus type 1 (HIV-1) vif gene, vifA45-2, which encodes a protein lacking 19 amino acids at the C terminus but which is fully functional in supporting HIV replication in non-permissive cells has been described previously. By employing newly generated anti-VifA45 serum, further properties of VifA45 and its full-length counterpart, VifA45open, in comparison to Vif from HIV strain BH10 are reported in permissive HeLa and COS-7 cells. The results obtained using confocal microscopic localization studies and in vitro binding assays do not support a requirement for the direct interaction of HIV Gag with Vif. Furthermore and in contrast to previous conclusions, detergent solubility analyses do not demonstrate a role for the C terminus of Vif in mediating localization to the fraction containing cellular membrane proteins. Localization of Vif from HIV strain BH10 to perinuclear aggregates in a small fraction (about 10%) of transfected HeLa cells has been previously reported. The intermediate filament protein vimentin colocalizes to these structures. In contrast, VifA45 and VifA45open form perinuclear aggregates in nearly all transfected HeLa cells; vimentin as well as the cytoskeletal-bridging protein plectin, but not the microtubular protein tubulin, become relocalized to these structures. Interestingly, in COS-7 cells, all of the functional Vif proteins tested (Vif from strain BH10, VifA45 and VifA45open) predominantly localize in the cytoplasm but still induce dramatic aggregation of vimentin and plectin, i.e. in these cells the respective Vif proteins are influencing intermediate filament structure in the absence of colocalization.

Tryptophan 95, an amino acid residue of the Caprine arthritis encephalitis virus vif protein which is essential for virus replication

The Caprine arthritis encephalitis virus (CAEV) vif gene was demonstrated to be essential for efficient virus replication. CAEV Vif deletion mutants demonstrated an attenuated replication phenotype in primary goat cell cultures and resulted in abortive infection when inoculated into goats. In this study, we determined the in vitro replication phenotype of five CAEV Vif point mutant infectious molecular clones and the ability of the corresponding in vitro translated Vif proteins to interact with the CAEV Pr55(gag) in the glutathione S--transferase (GST) binding assay. Here we show that (i) three of the mutants (S170E, S170G, S197G) behaved as the wild-type CAEV according to virus replication and Vif--Gag interactions; (ii) one mutant (Vif 6mut) was replication incompetent and bound weakly to GST-Gag fusion proteins; and (iii) one mutant (Vif RG) was impaired for replication while retaining its interaction properties. This mutant points out the critical importance of the CAEV Vif tryptophan residue at position 95 for efficient virus replication, defining for this lentivirus a functional domain unrelated to the Gag binding region.

Mutational analysis of the human immunodeficiency virus type 1 Vif protein

Lentivirus Vif proteins are potent regulators of virus infectivity. However, relatively little is known about the functional domains, peptide motifs, or residues of any Vif protein. In this report, we present the first extensive mutagenesis analysis of the 192-amino-acid human immunodeficiency virus type 1 (HIV-1) Vif protein. A large number of scanning missense (mostly alanine substitution) and deletion mutations were introduced into the HIV-1HXB3 vif gene, and the resulting proteins were evaluated for the induction of virus infectivity as well as subcellular localization. The results show that amino acids dispersed throughout Vif's linear sequence are important for function. However, because many of the inactive proteins also appear to be mislocalized, we suggest that many of them may actually be misfolded rather lacking an intracellular targeting signal. Interestingly, disruptions within an internal region spanning residues 114 to 146 give rise to mutant proteins that either retain function or are inactive but are not substantially mislocalized. We therefore speculate that this region, which harbors two essential cysteine residues and one essential serine residue, may contain aspects of a putative Vif effector domain.

Human immunodeficiency virus type 1 Vif-derived peptides inhibit the viral protease and arrest virus production

Human immunodeficiency virus type 1 (HIV-1) Vif protein is required for productive HIV-1 infection of peripheral blood lymphocytes and macrophages in cell culture and for pathogenesis in the SCID-hu mouse model of HIV-1 infection. Vif inhibits the viral protease (PR)-dependent autoprocessing of truncated HIV-1 Gag-Pol precursors expressed in bacterial cells and efficiently inhibits the PR-mediated hydrolysis of peptides in cell-free systems. The obstructive activity of Vif has been assigned to the 92 amino acids residing at its N'-terminus (N-Vif). To determine the minimal Vif sequence required to inhibit PR, we synthesized overlapping peptides derived from N-Vif. These peptides were then assessed, using two in vitro and two in vivo systems: (i) inhibition of purified PR, (ii) binding of PR, (iii) inhibition of the autoprocessing of the Gag-Pol polyprotein expressed by a vaccinia virus vector, and (iv) inhibition of mature virus production in human cells. The peptides derived from two regions of N-Vif encompassing residues Tyr-30-Val-65 and Asp-78-Val-98, inhibited PR activity in both the in vitro and the in vivo assays. Thus, these peptides can be used as lead compounds to design new PR inhibitors.